Believe it or not, there are some foods that can help you to feel "good". Among them are nuts, like almonds and walnuts. Dark chocolate is also good as it contains something called flavonoids. Another feel good source. Here’s a list of them:
50 Foods That Make You Happy | Eat This Not That
Exercise is also good for helping you get a "high" and feel better all around. I can add some music to that, or some of your favorite things to do. A friend of mine once gifted me with a little plaque that says, "Do something you love to do every day" ( or something like that. Its in a box!)
But I really would recommend you talking to your doctor, being that this is out of the blue and there is no cause that you see for it. He may want to recommend something better, get to the bottom of what can be going on, perhaps something in your system that you're not aware of.
I hope you feel better, JPT.
The only true wisdom is in knowing you know nothing.